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Lilmike234

  • one year ago

what is the radius of a circle with the equation x^2+y^2+2x+4y-9=0

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  1. Nnesha
    • one year ago
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    standard form equation of the circle \[\huge\rm (x-h)^2+(y-k)^2=r^2\] where (h,k) is the center point and r =radius

  2. Nnesha
    • one year ago
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    so move the -9 to the right side

  3. jdoe0001
    • one year ago
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    do you know what a "perfect square trinomial" is? sometimes also just called a "perfect square"

  4. lilmike234
    • one year ago
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    Yeah I heard of it.

  5. zzr0ck3r
    • one year ago
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    \(x^2+y^2+2x+4y-9=0\\ x^2+y^2+2x+4y=9\\ x^2+2x+y^2+4y=9\\ (x+1)^2-1+y^2+4y=9\\ (x+1)^2+y^2+4y=10\) Now do something similar with the \(y^2+4y\).

  6. lilmike234
    • one year ago
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    So I would get 3 for my answer correct?

  7. zzr0ck3r
    • one year ago
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    Now look at what @Nnesha said

  8. lilmike234
    • one year ago
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    So my answer would be 6?

  9. zzr0ck3r
    • one year ago
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    \(x^2+y^2+2x+4y-9=0\\ x^2+y^2+2x+4y=9\\ x^2+2x+y^2+4y=9\\ (x+1)^2-1+y^2+4y=9\\ (x+1)^2+y^2+4y=10\\ (x+1)^2+(y+2)^2-4=10\\ (x+1)^2+(y+2)^2=14\\ (x+1)^2+(y+2)^2=(\sqrt{14})^2\)

  10. lilmike234
    • one year ago
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    So my answer should be 3.74 correct ?

  11. zzr0ck3r
    • one year ago
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    how did you get that?

  12. lilmike234
    • one year ago
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    I square rooted 14

  13. zzr0ck3r
    • one year ago
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    right

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